The present invention relates to an optical connector and, more particularly, to a ferrule for an optical connector that connects optical fibers to each other.
FIG. 10A shows a ferrule for an optical connector disclosed in Japanese Patent Laid-Open No. 62-276513 (Reference 1), and FIG. 10A shows this ferrule from which its upper and lower molds are removed.
As shown in FIG. 10B, a press plate 74 made of a silicon material is adhered to a silicon support plate 73 having an upper surface formed with V-shaped optical fiber guide grooves and guide pin grooves, thereby forming optical fiber guide holes 81 and guide pin holes 82 each having a regular-triangular cross section. Optical fibers 75 are inserted in the optical fiber guide holes 81, and closed with upper and lower molds 72 and 71, as shown in FIG. 10A. Molding with a resin 76 is performed including the optical fibers 75, thereby fixing the optical fibers 75.
Japanese Patent Laid-Open No. 62-276514 (Reference 2) also discloses a technique similar to that of FIGS. 10A and 10B.
FIG. 11A shows a ferrule for an optical connector disclosed in Japanese Patent Laid-Open No. 3-179406 (Reference 3), and FIG. 11B shows the main part of the same.
As shown in FIG. 11A, a ceramic support plate 90 having an upper surface formed with V-shaped optical fiber guide grooves and guide pin grooves is buried in a molded resin 93. Optical fiber guide holes 91 and guide pin holes 92 each having a circular cross section are formed in the molded resin 93 with reference to these optical fiber guide grooves and guide pin grooves.
More specifically, the optical fiber guide holes 91 and guide pin holes 92 extend from the interior of the molded resin 93 and open in a side end face 94 of the molded resin 93 through the optical fiber guide grooves and guide pin grooves of the ceramic support plate 90. As shown in FIG. 11B, the side end face 94 of the molded resin 93 is separate from a side surface 95 of the ceramic support plate 90 by a distance L.
Japanese Patent Laid-Open No. 3-179405 (Reference 4) also discloses a technique similar to that of FIGS. 11A and 11B.
In the prior art of FIGS. 10A and 10B or FIGS. 11A and 11B, the grooves are formed in the silicon support plate 73 or ceramic support plate 90, and the optical fiber guide holes 81 or 91 and the guide pin holes 82 or 92 are formed at the predetermined portions of the silicon support plate 73 or ceramic support plate 90.
In the prior art of FIGS. 10A and 10B, when optical connectors are to be connected to each other, the distal ends of the optical fibers 75 cannot be made to project by a small amount (e.g., 0.5 .mu.m to 1 .mu.m) from the side end face of the ferrule in order to bring the distal ends of the optical fibers 75 into direct contact with each other.
More specifically, the projecting shape of the optical fibers 75 can be obtained by subjecting the side end face of the ferrule to optical mirror surface finishing by means of buffing (buff polishing). The mirror surface finishing is also called PC (Physical Contact) polishing. According to mirror surface finishing, in order to decrease connection loss of propagation light by Fresnel reflection, the distal ends of the optical fibers 75 are made to project from the side end face of a ferrule by a small amount, and the end faces of opposing optical fibers 75 are brought into direct contact with these projecting distal ends, thereby realizing a low connection loss.
This buff polishing (PC polishing) uses a polishing medium, e.g., diamond abrasive grains. The distal ends of the optical fibers 75 cannot be made to project by a small amount unless the end face of the ferrule is formed of only a resin (plastic) softer than the optical fibers 75.
This is due to the following reason. When the difference in hardness between the side end face of the ferrule and the optical fibers 75 is small, like the conventional ferrule shown in FIGS. 10A and 10B, or when a ceramic material or silicon harder than the optical fibers 75 exists, the finished surface including the optical fibers 75 may become flat, or inversely the distal ends of the optical fibers 75 may be recessed.
In the prior art shown in FIGS. 11A and 11B, the side end face of the ferrule is formed of only the molded resin 93 to be separate from the side surface 95 of the ceramic support plate 90 by the distance L.
Generally, a coefficient of linear expansion is large in a resin and small in a ceramic material or silicon. Hence, after a high-temperature molded resin is set, if it is cooled down to room temperature (temperature of the environment where the connector is to be used), a difference in size occurs between the resin and ceramic material.
For this reason, the optical fiber guide holes 91 and guide pin holes 92 appearing in the side end face of the ferrule cannot reflect the high-precision size of the ceramic support plate 90 serving as the core pin guide member.
More specifically, due to the difference in coefficient of linear expansion between the ceramic support plate 90 and molded resin 93, the hole pitch error may occur at the resin portion corresponding to the distance L between the side surface of the ceramic support plate 90 and the side end face 94 of the molded resin 93.
In the prior art shown in FIGS. 11A and 11B, when L=0 is set, i.e., when the side surface 95 of the ceramic support plate 90 is set to coincide with the side end face of the ferrule, the distal ends of the optical fibers cannot be made to project from the side end face of the ferrule by a small amount in accordance with buffing in the same manner as in the prior art of FIGS. 10A and 10B. Accordingly, it becomes impossible to realize a low connection loss by bringing the distal ends of opposing optical fibers into direct contact with each other.